A number of components are initially cast or forged into an approximate shape for the final finished component. Such an approach allows ease of manufacture as well as potential crystallography and material treatment to be achieved conveniently. The forged component such as a turbine disc is then machined appropriately in order to achieve the final component shape and surface finish. Generally the original forged component only provides a rough approximation to the final finished shape and so a significant proportion of the forged material must be removed in order to achieve the desired finished shape.
Machining of the forged component is typically through milling, turning or broaching whereby material is removed from the rough forged component until the desired finished shape is achieved. For example, Heyligenstaedt four-axis turning machines are known for providing the final machining of rough forged components into desired compressor discs. Unfortunately, these machines are designed for high accuracy operation such that multiple abutment clamping of the component is necessary and normally a datum such as a flat surface is initially provided to the component to ensure surety of position and therefore machined accuracy in the final product. Such robust and accurate assembly as indicated is highly beneficial with regard to high accuracy machining processes but with regard to machining initially rough forged components may be detrimental.
It will be understood that forged components generally retain residual stresses arising from the forging or casting process. These residual stresses cannot be relieved in the above forged component due to the high strength clamping inherent in machines such as Heyligenstaedt four-axis turning machines for accurate forming. In such circumstances, when the multi abutment clamping is released the final machine component may become distorted as these residual stresses are then relieved. Such distortion clearly detracts from the desired shape profile for the component in its finished state.